System and device for exploration of the intrathoracic ventilatory mechanism

ABSTRACT

A system and process for exploration of the intrathoracic ventilatory mechanism producing a signal y (V + lambda dV/dt) IN WHICH V the volume displaced in the mouth of a patient, and lambda is an adjustable parameter. The signal y is recorded on an oscilloscope in dependence on Delta p which is a signal indicating variations in oesophageal pressure. The parameter lambda is adjusted at the oscilloscope so that the loop representing y is closed in a straight line with the slope of the straight line giving compliance C and lambda /C giving the intrathoracic resistance.

United States Patent [1 1 Bargeton et al.

[4 1 Sept. 2, 1975 1 SYSTEM AND DEVICE FOR EXPLORATION OF THE INTRATIIORACIC VENTILATORY MECHANISM [75] Inventors: Daniel E. L. Bargeton, Paris; Paul A.

A. Monzein, Sceaux; Jean Y. V. Durand, Bagneux, all of France [73] Assignee: Institut National de la Sante et de la Recherche Medicale, France 221 Filed: Mar. 25, 1974 21 Appl. No.: 454,711

[30] Foreign Application Priority Data Mar. 23, 1973 France 73.10597 [52] US. Cl. 128/2.08 [51] Int. Cl. A61B 5/08 [58] Field of Search 128/208, 2.07, DIG. 29

[56] References Cited UNITED STATES PATENTS 3,480,006 11/1969 Schomber 128/208 3,713,436 l/1973 Hardway, Jr 128/208 OTHER PUBLICATIONS Comroe, et al., Design of Body Plethys. for Studying Cardiopol. Physioly, .1. of App. Phys, Vol. 14, 1959, May, pp. 439-444.

Dubois et al., Method for Measuring Airway Resist. in Man Using Body Plethys, J. of Clin. Investigation, Vol. 35, 1956, pp. 327-335.

Gulesian, Instr. for Measurement of MEFV Parameters," IEEF, Trans. on Bio-Med. Eng, Sept, 1971, pp. 378-382.

Jaeger et al., Measurement of Air Resist. with Body Plethys, .1. of App. Phys, Vol. 19, No. 4, July, 1964, pp. 813-820.

Primary Examiner-Richard A. Gaudet Assistant ExaminerLee S. Cohen Attorney, Agent, or FirmCraig & Antonelli [5 '7] ABSTRACT A system and process for exploration of the intrathoracic ventilatory mechanism producing a signal y (V )tdV/dt) in which V the volume displaced in the mouth of a patient, and A is an adjustable parameter. The signal y is recorded on an oscilloscope in dependence on A p which is a signal indicating variations in oesophageal pressure. The parameter A is adjusted at the oscilloscope so that the loop representing y is closed in a straight line with the slope of the straight line giving compliance C and A/C giving the intrathoracic resistance.

3 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION The present invention relates to a system and process for exploration of the intrathoracic vontilatory mechanism, and a corresponding device for applying the sys tem.

The exploration is based on the following considerations:

Ventilatory mechanics considers the ventilatory system as a linear system of the second order. In addition, it is possible to show and verify by experiments that, during respiration in the rest condition, the inertia forces can be neglected, thus reducing the system in question to the first order.

Obvious theoretical reasons (non-laminar flow in the air passages, deformation of the tissues not being in accordance with Hookes law, non-newtonian viscosity of the tissues) show that the linear hypothesis is only an approximation, but experience shows that this approximation is excellent in the normal subject in the rest condition, and in most cases is acceptable in the case of a sick person.

Under these conditions, on writing that the motor pressure A p developed by the respiratory muscles balances the effect of the return forces (resilient forces and surface tension) and resistance forces (aerodynamic and tissular), we have the equation, considering the intrathoracic organs, excluding the wall:

E (Vp Vr) R (IV,,/dt Ap in which equation:

E is the intrathoracic elastance R is the intrathoracic resistance Vp is the pulmonary volume, Vr is the relaxation volume. Or again, in dependence on compliance C 1/15 In order to have only values which can be directly measured, we take for A p the variations is oesophageal pressure, as given by a small balloon or gas-bag, and for the volume V displaced at the mouth:,

V being the pulmonary volume at the beginning of inhalation.

In this way, the variations in intrapulmonary pressure are neglected, and the change in state in the inhaled air is considered as instantaneous, passing from the ambient conditions (ATPS) to the alveolar nditions (BTPS). The signal dV/dt is provided by a pneumotachograph (PTG), which signal integrated with respect to time provides V.

We then have:

In the present state of the known art, a conventional process comprises recording, in respect of time, A p

and V and its derivative dV/dl. For two points at zero flow ill 1/! 'D we have:

v, V, A];2 AI),

and for two points of equal volume V AIM AI) R 11v, (114,

Another conventional process comprises recording on a track, V in dependence on A p; and on another track dV/dt in dependence on A p. On the loop in respect of V, the two points at zero flow are determined by means of their horizontal tangents, and compliance is the slope of their diameter; while on the loop in respect of dV/dt the two points of equal volume are taken, which makes it possible to calculate R.

However, these two conventional processes suffer from various disadvantages:

1. Only two points on the cycle are used, and not the entire information.

2. Determination of these points is highly subjective because of the noise which is superimposed on the trace. This noise is inevitable as it is not caused by instrumentation, but is of biological origin (in particular cardiac pulses). For this reason the noise-signal ratio is often very poor and determining the zeroflow points, the trace of tangents to the loop, and determining points of equal volume, involve a great deal of arbitrariness.

3. Respiration, like most biological phenomena is not periodic but pseudo-periodic. Even when a subject is still, successive respiratory cycles are not identical. Selecting a cycle as representative of the mean condition is therefore fairly arbitrary. Satisfactory determination of the mean condition should be based on observing a large number of cycles, which is not done because of the laborious nature of such a procedure.

4. No arrangement is provided for correct calibration of the PTO, and the change in inhalation-exhalation calibration factor is not known.

5. Inhalation and exhalation cannot be observed separately.

6. The processes involved are slow and laborious.

SUMMARY OF THE INVENTION The aim of the invention is to overcome the above mentioned disadvantages.

Briefly, the system and process according to the invention employs a signal and v is recorded in dependence on A p on an oscilloscope with A being a regulatable parameter which is regulated on the oscilloscope so that the loop representing v is closed in a straight line, and then A RC, and the slope of the straight line gives C, hence It will be noted that closing a loop in a straight line is a particularly straight-forward and precise phenomenon in oscilloscopy. Moreover, it is sufficient to regulate to zero to produce a loop whose surface area measures the intrathoracic ventilatory work per cycle.

The invention also includes means for permitting gain regulation, calibration and separate observation of the two phases of respiration.

For calibrating the pneumotachograph (PTG) under alveolar conditions (BTPS):

The PTG supplies a signal which is proportional to the flow (IV/d1, the calibration factor being proportional to the viscosity of the gaseous mixture which passes through it. This viscosity depends on temperature and the water vapor content, and is therefore not the same for inhaled air and for exhaled gas which is water-vapor saturated at the temperature of the body. It is impossible to know beforehand the temperature of the gas in the PTG, because of the heat exchanges which occur between the gas and the walls. In addition, as viscosity is not an additive property, it is impossible to deduce the viscosity of the gaseous mixture from the viscosities of its components. It is therefore impossible to envisage beforehand how the calibration factor of the PTO is going to vary as between inhalation and exhalation. It is only possible to do this on an empirical basis, on gaseous mixtures which are identical to the inhaled air and the exhaled gas. It is known for this purpose to provide a pump for calibration under alveolar conditions. A cylindrical vessel contains water which is maintained at a temperature of 37 by means of a thermostat. A turbine provides for heat and moisture exchanges between the water and the air which it contains. A plunger piston varies the volume of the vessel. The pneumotachograph to be calibrated is mounted on a pipe which is fixed to the cover of the vessel, so that ambient air passes through the pneumotachograph during inhalation when the piston is moved downwardly, while gas under alveolar conditions passes through the pneumotachograph during exhalation" when the piston is raised.

BRIEF DESCRIPTION OF THE DRAWING The accompanying single FIGURE illustrates an apparatus for applying the system and process according to the invention, given by way of non-limiting example.

DESCRIPTION OF THE PREFERRED EMBODIMENT The pneumotachograph 1 supplies the signal +dV/dt to a gain regulating potentiometer 3 having a slider which supplies a signal to a circuit 5 for detecting the sign of dV/zlL'During inhalation, the circuit 5 closes its switch contacts 7 which, by way of a switch 9, feeds a relay 11. The slider of the potentiometer 3 also supplies the signal to a potentiometer 13 for correction of gain upon exhalation, its effect upon inhalation being nullified by being bridged by a working contact 15 of the relay II. The slider of the potentiometer l3 feeds an operational amplifier 17 connected as an integratorinverter, at whose output the signal V is produced. The slider of the potentiometer 13 also supplies the signal to a single-pole change-over switch 19 having three positions which acts as a gain change-over means and which supplies the signal with gain 0, or with gain 1, or with gain 10, to an inverter amplifier 21 which supplies a potentiometer 23 for displaying the regulatable parameter A. At the slider of the potentiometer 23 there is therefore obtained the signal (1V A (II The two signals V and (IV A 1/! are added by an inverter-summing means 25, at the output of which there is obtained the signal (IV V\' V )t T The signal passes either by way of a rest contact 27 of the relay 11 and a cut-out switch 29, or a working contact 31 and a cut-out switch 33, and passes to the vertical active plate Y of an oscilloscope 35. The gasbag 37 passes the signal A p to the horizontal active plate X of the oscilloscope 35, which oscilloscope may be of the type having a long-persistance screen, provided with a so-called Polaroid immediate photographic apparatus, etc.

The PTG 1 is mounted on a calibration pump (not shown), and calibration is effected not with respect to flow but with respect to volume, the integrator 17 having a time-constant of I second. The switch 19 having suppressed the input into the summing means 25 of the signal (1V M1, enables V to be registered with respect to time on the oscilloscope 35. The sign detector 5 cuts in the potentiometer 13 onto the signal dV/dt for exhalation, and short circuits it for inhalation. The cut-out switches 29 and 33 are closed so as to record inhalation and exhalation. As the calibration pump neither produces nor consumes gas, the same mass of air passes through the PTG during inhalation under conditions ATPS and during exhalation under conditions BTPS.

The potentiometer I3 is acted upon so that the mean value of the signal is zero. This calibration correction is much more precise by observing volume than by observing flow, as any inequality in calibration is integrated in each cycle, and is rendered visible even if it is small. The potentiometer 3 is then acted upon, to produce the desired value of the deflection observed for a known volume (500, 750 or 1000 ccm).

For the possibility of separately observing inhalation and exhalation:

In the normal condition, the resistance is substantially the same for inhalation and for exhalation, at least in the rest condition. In the case of a sick person, this may be different, and there may therefore be an advantage in observing inhalation and exhalation separately. This is permitted by the switches 27 and 31 associated with the relay 11 which is actuated by the detector circuit 5. Finally, in the sick person, substantial values of R can be observed. The changeover switch 19 makes it possible to use the inverter 21 with a gain of 10, and it is therefore possible to observe time constants RC ranging up to seconds, which covers all the needs arising in pathological investigation.

It is clear from the foregoing description that, compared with the conventional procedure, the procedure using the device according to the invention has the following advantages:

1. The entire information supplied by the cycle under observation is used.

2. Because of the persistance of the screen, the information supplied by several successive cycles is employed. The values determined for R and C are therefore representative of the mean condition of the passive intrathoracic ventilatory system.

3. The eye is very sensitive to the motion of a straight line and, on a noisy signal, can much better determine a straight line than a curve or a loop.

4. The use of a memory oscilloscope makes it possible to dispense with photographic recording.

5. Correct calibration of the PTG in the two phases of respiration is carried out with accuracy and rapidly.

6. The entire procedure involved is rapid, simple and includes little in the way of subjective elements.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It should therefore be understood that within the scope of the apended claims, the invention may be practiced otherwise than as specifically described.

We claim:

1. A system for exploring the intrathoracic ventilator mechanism of a subject, comprising means for supply ing a signal A p of the variations in oesophageal pressure, pneumotachograph means for supplying a signal dV/dt of the derivative with respect to time of the vol ume V displaced at the mouth of the subject, integrating circuit means for receiving the signal dV/tlt and supplying a signal V, summing circuit means for receiving the signal dV/dt and the signal V for supplying a signal in which A is a regulatable parameter, and oscilloscope means having a horizontal input for receiving the signal A p and a vertical input for receiving the signal y, the parameter A being regulated so that the loop displayed on the screen of the oscilloscope means is closed in a straight line, the slope of the straight line giving the compliance C and the quotient of the division of the parameter A by the compliance C giving the intrathoracic resistance R, and further comprising gain regulating potentiometer means for receiving the signal dVdr from the pneumotachograph means and providing an output signal on the slider thereof, detector circuit means supplied with the output signal of the potentiometer means for detecting the sign of the signal u'V/dt, relay means having two working contacts and a rest contact and being responsive to the detector circuit means for closing the working contacts and opening the rest contact during inhalation of the subject, gain correcting poten tiometer means for correcting gain during exhalation of the subject, the gain correcting potentiometer means being supplied with the output signal of the gain regulating potentiometer means and providing an output signal on a slider thereof, the gain correcting potentiometer means being shoit-circuited by the closing of one of the working contacts of the relay means during inhalation of the subject, the integrating circuit means including an integrator for receiving the output signal of the slider of the gain correcting potentiometer means and providing the signal V at the output thereof, an inverter at the output of the integrator providing a signal V, the summing circuit means including a single-pole change-over switch having three positions and connected to the slider of the gain correcting potentiometer means, an amplifier-inverter circuit connected to the change-over switch, a potentiometer means connected to the amplifier-inverter circuit for setting the regulatable parameter A and providing a signal of and an inverter-summer means for receiving the signals -V and and providing the signal to the vertical input of the oscilloscope means through the other of the working contacts or the rest contact of the relay means.

2. A system according to claim 1, wherein the oscillo scope means displays on the screen a loop in which the surface of the loop for the value zero in the parameter A is a measure of the intrathoracic ventilatory work per cycle of the subject.

3. A system according to claim 1, further comprising a first cut-out switch in series with the rest contact of the relay means and a second cut-out switch in series with the other of the working contacts of the relay means, the first and second cut-out switches receiving the signal y from the inverter-summer means and being connected to the vertical input of the oscilloscope means, and the means for supplying A 2 signal including a gas-bag means for supplying the A 2 signal to the horizontal input of the oscilloscope means. 

1. A system for exploring the intrathoracic ventilator mechanism of a subject, comprising means for supplying a signal Delta p of the variations in oesophageal pressure, pneumotachograph means for supplying a signal dV/dt of the derivative with respect to time of the volume V displaced at the mouth of the subject, integrating circuit means for receiving the signal dV/dt and supplying a signal V, summing circuit means for receiving the signal dV/dt and the signal V for supplying a signal
 2. A system according to claim 1, wherein the oscilloscope means displays on the screen a loop in which the surface of the loop for the value zero in the parameter lambda is a measure of the intrathoracic ventilatory work per cycle of the subject.
 3. A system according to claim 1, further comprising a first cut-out switch in series with the rest contact of the relay means and a second cut-out switch in series with the other of the working contacts of the relay means, the first and second cut-out switches receiving the signal y from the inverter-summer means and being connected to the vertical input of the oscilloscope means, and the means for supplying Delta p signal including a gas-bag means for supplying the Delta p signal to the horizontal input of the oscilloscope means. 